GB2097599A - Improvements relating to units provided with removable portions - Google Patents

Abstract

In a unit comprising a plastics sheet having one or more removable portions, a fracture line of discrete shallow indentations is provided on the portion so that it may be removed. In the embodiment, cable trunking, the walls 2 incorporate separate fingers 6 which can be broken away as at 8 to provide space for leading in or out cables housed within the trunking. Each finger can be broken off readily by flexing about the weakened area formed by the indentations 7 &cirf& This ensures that the break occurs where required but does not allow the fingers to break off inadvertently due to a sharp impact. <IMAGE>

Description

SPECIFICATION Improvements relating to units provided with removable portions This invention is concerned with the requirement for providing removable portions on units incorporating or comprising a sheet of plastics material. For example, the unit may be a channel member to be used as cable trunking and having a number of individual fingers along the side walls which can be removed to provide large openings through which cables may project. It has been common practice with such cable trunking to provide scoring in the form of a continuous line at the base of the fingers where it is to be removed. Unfortunately, however, the act of scoring of the material so alters the crystalline structure of the plastics material that it becomes very brittle and may therefore break readily if subjected to a sharp knock.Fingers may therefore be broken off inadvertently in positions where this is not required and in particular parts may break off trunking units whilst they are being delivered to a customer. Scoring is therefore looked on as a dubious method providing the means for enabling such fingers to be broken out. If scoring is omitted then it may still be possible to break off the finger by flexing it back and forth but the effort required is much greater than when scoring is provided and the breakage line may not be in the desired position and could leave jagged portions which might cut into the insulation of cables passing through a gap left when the finger is removed.

However it has now been discovered that the problem of premature breaking off of a finger in cable trunking which occurs when a continuous scoring line is provided can be substantially alleviated by a different method of scoring. It is anticipated that units of quite different construction may at times require the provision of parts which may be broken off as required and so the invention relates to various other types of units as well as cable trunking.

In accordance with the invention, there is provided a unit comprising or including a sheet of plastics material having one or more removable portions, a fracture line for each removable portion being provided by a line of discrete shallow indentations at the join between the removable portion and the rest of the unit.

It seems that a provision of a number of discrete indentations leaves sufficient material of the full thickness of the sheet to ensure that a premature fracture is unlikely to occur. However, when the removable portion is flexed about the fracture line, the presence of the indentations will tend to ensure that fracture occurs along the line defined by the indentations, namely in the desired position.

Ideally the shallow indentations will have a length approximately equal to or less than the distance between two adjacent indentations. It is preferred that the shallow indentations should not extend more than half way through the thickness of the material. In particular it is desired that the depth of the indentations should be about one quarter or less, preferably about one tenth, of the thickness of the material in which they are formed.

The unit may be in the form of cable trunking whose side wall(s) incorporate independant fingers, at least some of which are removable and incorporate said fracture line. In this case it is preferred that the fracture line should be formed to the inside of the trunking side wall.

The invention may be performed in various ways and a preferred embodiment thereof will now be described, with reference to the accompanying drawing, in which: Figure 1 is an end view of a portion of cable trunking; and Figure2 is a cross-sectional view on line ll-ll of Figure 1 illustrating the incorporation in the trunking of the inventive feature of this invention.

The trunking section shown in the drawings comprises a base portion 1 and two side walls 2 provided at their free ends with flanges 3 which will receive a cover member (not shown). A bundle of cables will pass through a space 4 defined by the trunking and individual cables may be lead out through openings 5 in the trunking side walls. These openings are defined by cut-away portions of individual fingers 6 which together define the sidewall 2. On the interior surface of each finger 6, towards the base thereof, there is formed a line of discrete shallow indentations 7. In this instance the side walls have a thickness of about 2 mm and the indentations are formed to a depth of about 0.25 mm. In this particular example the indentations 7 have a length which is about two thirds of the distance between adjacent indentations.

If it is desired to provide a large opening in the side wall of the trunking for a number of cables (or a particularly large cable) to be lead out at one point, one or more of the fingers 6 may be broken out. This is achieved by flexing a finger 6 back and forth about the fracture line defined by the indentations 7 at the base of the finger. The plastics material will be weakened (due to a change in crystalline structure) at each of the indentations 7 and so this weakness will tend to be transferred to adjacent portions of the plastics material resulting eventually in the finger being fractured off generally along the line defined by the indentations 7 as illustrated at 8.

Generally it is envisaged that the indentations 7 will be formed by scoring the preformed trunking unit by passing a toothed wheel over the surface of the material (and providing a surface, such as a pressure wheel, to the other side of the material).

The spacing and depth of the indentations formed in the plastics material will of course depend upon the spacing and the extent of projection of the teeth on the toothed wheel and can therefore readily be predetermined. The ease with which fracture will occur along the line defined by the indentations will depend upon the extent of the spacing and the depth of these indentations so that a particularly desired degree of ability to fracture can be built in for a specified purpose. By this means, it is possible to ensure that the cable trunking may readily be transported to a customer without risk of one or more of the fingers breaking off in transit under normal conditions. However the presence of the fracture line defined by the indentations 7 will enable the user to break out a finger 6 from the trunking in such a way that the finger breaks off at the desired position at its base.

CLAIMS (filed on 19.6.81) 1. A unit comprising or including a sheet of plastics material having one or more removable portions, a fracture line for each removable portion being provided by a line of discrete shallow indentations at the join between the removable portion and the rest of the unit.

2. A unit according to claim 1, wherein the shallow indentations have a length approximately equal to or less than the distance between two adjacent indentations.

3. A unit according to claim 1 or claim 2, wherein the shallow indentations do not extend more than halfway through the thickness of the material.

4. A unit according to claim 3, wherein the depth of the indentations is about one quarter or less, preferably about one tenth, of the thickness of the material in which they are formed.

5. A unit according to any one of claims 1 to 4, in the form of cable trunking whose side wali(s) incorporate independant fingers, at least some of which are removable and incorporate said fracture line.

6. A unit according to claim 5, wherein the fracture line is formed to the inside of the trunking side wall.

7. Acabletrunking unit substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. fracture line defined by the indentations 7 will enable the user to break out a finger 6 from the trunking in such a way that the finger breaks off at the desired position at its base. CLAIMS (filed on 19.6.81)

1. A unit comprising or including a sheet of plastics material having one or more removable portions, a fracture line for each removable portion being provided by a line of discrete shallow indentations at the join between the removable portion and the rest of the unit.

2. A unit according to claim 1, wherein the shallow indentations have a length approximately equal to or less than the distance between two adjacent indentations.

3. A unit according to claim 1 or claim 2, wherein the shallow indentations do not extend more than halfway through the thickness of the material.

4. A unit according to claim 3, wherein the depth of the indentations is about one quarter or less, preferably about one tenth, of the thickness of the material in which they are formed.

5. A unit according to any one of claims 1 to 4, in the form of cable trunking whose side wali(s) incorporate independant fingers, at least some of which are removable and incorporate said fracture line.

6. A unit according to claim 5, wherein the fracture line is formed to the inside of the trunking side wall.

7. Acabletrunking unit substantially as herein described with reference to the accompanying drawings.